Telephone system



Jan. 2-8, 1947. J. wlcxs 2,415,057

1 TELEPHONE SYSTEM Filed Feb. 9, 1945 11 Sheets-Sheet 1 r BRANCH EXCHANGE 5O DISTRIBUTOR e02 780 8 q LINE LOCAL LOCAL -SELEGTOR cmcun FINDER SELECTOR eol I: 1..

u I6 J80! 8 8 LOCAL COMBINATION OONNEDGTOR CONNECTOR L863 FIG. 13 R850 7 v 830x LINE I /-ae| JB7OJANS. @l u I A JBBO CALL BRANCH EXCH. 5O

F16 i MAIN EXCH. 2o ToLL-gwmoo a UNE F'6PER. swan |ooo| J [T303 m3 @T' cm.a4o ms GAL I CORD TOLL 830 .L SELECTOR J810 J880 cm. 301 330 02 p3 y mo OR ..=--s2| L 4ao TOLL TRANS c D aaoe CIR. 900

#320 TRUNK cm. 600 Hmo 307 LOCAL LOCAL SELBIO FIND. 805

LINE 319 1.00m. SEL. LINE TRUQKCIR 3|4 SW 3" g! ana 3:5 5:3 |'coMa-coNN.| LOCAL com 30 s20 L0. 3:0 F: A I 826 Q;

| INVENTOR. JOHN wlcKs BY 7 M,M,Ww%%

ATTORNEYS Jan. 28, 1947. J. WICKS 2,415,057

TELEPHONE SYSTEM Filed Feb. 9, 1945 ll Sheets-Sheet 2 FIG. 2

VFIG2 C482 FIG.4 FIG. 5 FIG. 6 FIG. 7 m9 FlG.l0 FIG. u FIG.I2 c485 FI.3 G 04 4 8 FIG l4 FIG.I3 3201 FIG.| v 0...

FIG, 3

LIJ q E MAIN F- C3l--il -I\lC5E 20 d O P TOLL BOARD 30o P302 304, .1303 .J 305 TOLL 33P- 1] -r SELECTOR 332 I r340 LINE. SELECTOR TRUNK SW. 3|: :7 314 335 0 3|; 3|2 ans LOCAL COMBINATION 3'6 CONNECTQR 308 CONNECTOR g n n, a (309 CAD'A'MO" ATTORNEYS Jan. 28, 1947. M 2,415,057

} TELEPHONE SYSTEM Filed Feb. 9, 1945 ll Sheets-Sheet 6 ATTORNEYS Jan. 28,1947. r J. WlC KS 2,

TELEPHONE SYSTEM I I Filed Feb. 9, 1945 1.1 Sheets-Sheet 7 H6] 9 CORD CIRCUIT 90o V945 95a\; L919 I 959/ I 975% 950 INVENTOR.

. JOHN WlCKS BY mfm wm ATTORNEYS Jan. 28, 1947. J w c s 2,415,057

TELEPHONE sYsTEM Filed Feb; 9, 1945 I 'llSheets-Sheet a FIG. 10

RIOSO POLAR 4? I020 RECALL DIAL THRQUEF 025 FLASHER i044 INVENTOR.

" JOHN WIGKS ATTORNEYS Jan. 28, 1947. J. w|c| s TELEPHONE SYSTEM Filed Feb. 9, 1945 gmo,

Cllll) I 11 Sheets-Sheet 9 mo I ERvlsoRY Clll2 v FIG, 11

INVENTOR. JOHN w cxs ATTORNEYS Patented Jan. 28, 19 47 UNITED STATES PATENT OFFICE 2,415,057 TELEPHONE SYSTEM John Wicks, Biloxi, Miss., assign'or to Automatic Electric Laboratories, Inc., Chicago, 111., a cornoration of Delaware Application February 9, 1945, serial No. %,912

27 Claims. l

The present invention relates to telephone systoxins in general and, more particularly, to improvements in the apparatus provided for setting up toll connections in an interexchange network including both 7 automatic and combined automatic and manual exchanges.

It is an object of the present invention to provide, in a telephone system of the character indicated, a novel arrangement whereby a toll operator in a niain automatic exchange or toll office may interconnect toll lines terminating at her position with subscriber lines which terminate in a combined manual and automatic private branch exchange, either with or without the assistance of the branch exchange operator.

According to another object of the invention, facilities are provided for selecting the interexchange trunk lines over either one of two paths and for determining in accordance with the path over which the trunk line is selected whether the toll connection is to be completed to the desired called subscriber line under the exclusive control of the toll operator or whether the toll connection is to be completed under the joint control of the toll operator and the branch exchange operator. V

It is another object of the invention to provide, in a telephone system of the character in dicated, a new and improved arrangement for transmitting various supervisory and control signals in two directions over the interexchange trunk lines.

The invention, both as to its organization and method of operation, together with other objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanyin drawings, in which Figure 1 illustrates the general arrangement of a telephone system embodying the invention; Fig. 2 illustrates the mode of combining Figs} to 14, inclusive, of the drawings to form a unified system; and Figs. 3 to 14, taken together, illustrate a telephone system having incorporated therein the features of the invention, as briefly outlined above. More specifically, Fig. 3 shows a schematic layout of the switching apparatus and the toll board 393' located in the main exchange 20; Fig. 4 shows the detailed circuits of the toll tr'unk circuit tilt) in the main exchange 263; Figs. 5, 6 and 7 show the detailed circuits of the toll transmission trunk circuit 666 in the branch exchange 5E1; Fig. 8 shows a schematic layout of the switching apparatus located in the branch exchange 5t; Figs. 9 to 12, inclusive, show 2 as; F g. shows the detailed circuits r the equipment for the manual line 838; and Fig. 14 shows the detailed circuits of the operator telephor'i e circuit associated with the cord circuit WEI. Referring now more'particular'ly to Fig. 1 of the drawings, the telephone system there illustrated comprises a nairrexchange 2i] and a private branch exchange The main exchange 20 term inates a number of automatic subscriber lines which may be interconnected with the automatic and mason subscriber lines terminatin in the lor'n'ch exchange 58, in the manner described in detail iiithe ccphdihg Berge ser application, Serial Nd.- 57-3;913,- filed 9, 1945. The main 2t also includes a toll switchboard 3% which terminates plurality of toll lines M9 from distant exchanges and which has access to toll switch train, in order that tell calls received from the distant exchanges may be extended either to main exchange subscribers or to the branch exchange subscribers. Facilities are also provided at the main exchange 26 whereby the subscribers thereat may call the toll board 3% in order that the toll operator thereat may complete toll connections to the subscribers served by the distant exchanges reached by way of the toll lines 3 l9.

The branch exchange 50 is provided with a toll switch train of the Strowger type, whereby the toll operator in the main exchange 2%! may extend connections to the automatic subscriber lines in the branch exchange 58. The branch exchange 59 is also provided with a manual switchboard Hliiu whereby the operator thereat may extend toll calls received from the toll operator at the main exchange to the branch exchange manual or automatic subscriber lines.

When a toll call is received over the toll line (H9 at the toll board 3063, the operator thereat ma extend the connection to the'line of substation A or Al iri th e nfoain exchange 20 by means of the plugififi t of the cord circuit Bill, the jack- J Hi5, the toll selefctor 339, and the combination connector 368; The toll operator may also extend a toll comiection received over the toll line 319 to the line of the automatic substation' A2 or A3 in the branch exchange Eilby nae of the plug 1 3M of the cord circuit till, the" jack 53555,- the toll selector 330, the trunk lirie 329, the" toll trunk circuit 466]", the interexchange trunk line no, the toll transmission trunk circuit Eiiil', the toll selector 8E5, and the combination connector 8 25. It should be noted that the toll operatdrmay' also" extend a toll connec tion to the line of the manual substation M in thebran'ch exchange 59 by means of the plug P304 of the cord circuit 301, the jack J305, the toll selector 330, the trunk line 321, the toll trunk circuit 400, the interexchange trunk line 480, the toll transmission trunk circuit 600, and the jack J'160 to the manual operator at the switchboard 1005, who in turn completes the connection by means of the cord circuit 900, the jack J 880, the line circuit 840, and the line 830 of the substation M. If the toll call received by the manual operator at the branch exchange 50 is intended for the line of the automatic substation A2 or A3, the operator thereat may also complete such a connection by means of the cord circuit 900, the jack J T10, the toll transmission trunk circuit BSO, the toll selector 815, and the combination connector 825.

When the local subscriber at the substation A in the main exchange desires to extend a toll call to a distant exchange reached by way of the toll line 319, the connection is extended by means of the line switch 311, the local selector 314, the trunk circuit 335, and the trunk line 340 to the jack J306 at the toll board 300, and. the operator thereat completes the connection by means of the cord circuit 301 to the desired distant exchange reached by way of the toll line 319, all in the same manner as has been explained in the previously mentioned Burgener application.

In the event that a subscriber in the branch exchange 50 desires to call a subscriber reached by way of the toll line 319, a connection is first extended to the branch exchange switchboard 1000. After obtaining the necessary information for completing the toll call the manual operator at the switchboard 1000 informs the calling subscriber that he will be recalled as soon as the toll connection is completed to the desired called subscriber. The manual operator now extends a connection over a special switch train to the toll board 300 and releases the connection, after giving the toll operator the necessary information for completing the toll connection. The circuits and apparatus for extending a connection from the calling branch exchange subscriber to the manual operator and from the manual operator to the toll operator are disclosed and described in detail in the previously mentioned Burgener application. After the operator at the toll board 300 obtains the desired called subscriber in the distant exchange, she completes the connection by recalling the original calling subscriber in the branch exchange 50, as will be more fully described hereinafter.

ToLL CALL FROM A DISTANT EXCHANGE TO THE AUTOMATIC SUBSTATION A3 IN THE BRANCH Ex- CHANGE 50 Having described in general terms the manner in which various toll connections are established, a more detailed description will now be given of the operation of the circuits and apparatus utilized in establishing the various connections. For this purpose it will be assumed that the operator at the toll board 300 has answered a toll call received over the toll line 319, by inserting the answer plug P302 of the cord circuit 301 into the jack J 303, and that the calling subscriber or operator, as the case may be, in the distant exchange desires to communicate with the subscriber at substation A3 in the branch exchange 50. It will also be assumed that the toll operator has inserted the call plug P304 into the jack J305 and has seized the toll selector 330. The operator may now actuate her calling device (not shown) in order to operate the selector 330, in a well known manner, to raise its wipers 331 to 334, inclusive, in a vertical direction to a level corresponding .to the digit dialed, after which the wipers are rotated automatically to select an idle toll trunk circuit.

It should be noted that the toll selector 330 may be controlled to select the toll trunk circuit 400 over either the trunk line 320 or the trunk line 321. Referring now to Figs. 3 to 14, inclusive, it will be noted that the trunk line 320 terminates in the fifth level of the bank contacts accessible to the wipers 331 to 334, inclusive, of the toll selector 330 and that the trunk line 321 terminates in the sixth level. Accordingly, when the toll operator dials the digit 5 and thereby selects a toll trunk circuit, such as 400, over a trunk line, such as 320, the toll transmission trunk circuit 600 in the branch exchange is automatically controlled to direct the connection to the toll switch train in the branch exchange 50.

The toll operator may then directly control the toll switch train in order to extend the call to th desired automatic subscriber line.

If the toll operator should find it necessary to call the branch exchange operator in order to complete a desired toll call, she may dial the digit 6 whereupon a toll trunk circuit, such as 400, is seized over a trunk line, such as 321. The toll transmission trunk circuit 600 in the branch exchange 50 now functions, in a manner to be fully explained hereinafter, to extend the connection to the manual switchboard 1000. When the manual operator at the switchboard 1000 receives such a call, she may complete it by way of the cord circuit 900, either to a manual subscriber line, or by way of the toll transmission trunk circuit 600, the toll selector 815, and the combination connector 825, to an automatic subscriber line.

It will be assumed that the digit 5 was dialed by the toll operator and that the trunk line 320 is the one selected by the Wipers 331 to 334, inclusive, of the toll selector 330, whereupon ground potential is applied from the toll selector 330, by way of the wiper 334, the conductor C485, and the contacts 423, one branch of the circuit extending by way of the contacts 454 and the winding of the automatic relay R460, to battery, and the other branch of the circuit extending by way of the contacts 445 and the winding of the seizure relay R430, to battery. As a further result of the engagement of the wipers 331 to 334, inclusive, with the trunk line 320, a loop circuit is completed including the cord circuit 301, the plug P304, the jack J305, the toll selector 330, the wipers 331 and 332, the conductors C481 and C482 of the interexchange trunk line 480, the contacts 522 and 524, and the lower and upper windings of the pulse relay R640, to battery and ground respectively. The relay R640 operates over the above traced loop circuit to control the toll transmission trunk circuit 600, in a manner to be explained hereinafter.

When the above mentioned circuit for the automatic relay R 260 is completed, the relay operates and, at its contacts 453, prepares a circuit for subsequently operating the relay R440; and, at its contacts 461 and 462, it transfers the conductors 0484 from battery, through the winding of the operator relay R350, to direct ground, in order to mark the toll trunk circuit 400 busy in the banks of the selectors having access thereto. When the relay R430 operates over the above mentioned circuit, at its contacts 431, it opens a '5 point in an incomplete circuit for applying resistance battery by way of conductor C481 to the control relay R lill; and, at its contacts 432,

it prepares a point in an incomplete circuit for applying ground potential by way of conductor 04 .81 to the control relay hilt.

Attention is directed to the fact that the conductor C483 of the interexchange trunk line 439 is the control conductor over which the duplex relays R llt and Riilll are controlled in order to perform various operations in the main and branch exchanges. At the present time the windings of the above mentioned relays are shunted over a circuit which may be traced from ground, by Way of the contacts 95i and ltl, the conductor can, the lower winding of the relay Rt'iil (the upper winding of this relay being connected to ground by way of the resistance M2), the conductor C453, the lower winding ofthe relay REIB (the upper winding of this relay being connected to ground by way of the resistance M4), the conductor C553, and the contacts 555, E and 526, to ground. Since the above traced circuit, including the windings of the relays Reid and Rtlfi, is traced from ground to ground, the relays remain in their normal positions, and it will be understood from a further description of the operation of the system that signals may be transmitted over this circuit in both directions between the main and the branch exchanges to perform various supervisory and control operations.

When the previously traced loop circuit is completed for the pulse relay Rttil, the relay operates at its contacts 643, it applies battery potential by way of the high resistance 5'52, the winding of the relay Bold, the winding 5% of the repeating coil E56, the contacts 569, set and. til, to the conductor CW2 to prepare a point in the circuit for controlling the selector M5; at its contacts E42, it completes an operating circuit for the hold relay Retail; and, at its contacts 6%, it opens a point in an incomplete circuit for subsequentlyoperating the relay R635. The relay R 558, upon operating, at its contacts 65!, completes an operating circuit for the hold relay At its contacts 362, .the relay Rfiiiil upon operating, closes a point the incomplete for the relay and, at its contacts see, it completes an cpcr cg circuit for the relay uses which may be traced from ground, by way of the contacts and E32, and-the winding of the relay to c 'tery, and, at the same time, ground potential. is sitel'lded by way of contacts 853, 622, [tit an i365, conductor Cbtl', and contacts @lQQto the conductor Cite and by way of contacts and 6'53, to the conductor one. The glOllild potential applied to conductors Cit? and Cit-2- prepares the selector 555 for subsequent operation. -oe relay Riifiil, at its contacts 66 i, also applies ground potential by way of the winding of the re y the winding 55% of the repeating coil the contacts tit and 5 35, to the conductor Clsli, to prepare a point in the circuit for controlling the selector M5.

The relay Riitil operates over the above traced circuit and, at its contacts 55M, applies the operating ground potential for the relay Rbtil to the conductor At its contacts 555, the relay R550 opens a point in the incomplete circuit for the switching reiay Refit; at its contacts 5&2, it places a resistance in series with the conductors 0'83! and C'ieZ; and, at its contacts 56! and 563, it disconnects the windings sec and 555,

of therepe'ating coil 55%], and the battery and ground potentials, applied thereto by way of the windings of the relays R557 and new, from the conductors Gill! and C182. When ground po- 5 tential is applied to the conductors C 683 and C184 and when the resistance 515 is connected in series with the conductors are: and C782, the selector 8&5 is seized, in a well known manner, and may respond to impulses transmitted thereto under the control of the pulse relay R649.

The operator at the toll board $5M! may now actuate the dial thereat in accordance with the next digit of the called subscriber number and, as a result thereof, the pulse relay R640, in the toll transmission trunk circuit 661], at its contacts Ml repeats the impulses comtituting the dialed digit, by opening and closing the loop circuit extending to the selector M5. The first time the relay R-ttilre'stores to normal during impulsing, at" its contacts E5 23, it completes a circuit from ground, by way of the contacts 663 and 562 for operating the relay R630; at its contacts it opens the circuit of relay R659; and, at its contacts Mi, it interrupts the loop circuit in order to transmit the first pulse to the selector 395. Since the relay R650 is of the slowto-release type, it remains in its operated posi tion during impulsing. The relay R53i3, upon operating over the above traced circuit, at its contacts 63!, completes a holding circuit for itself from ground at contacts 5615, thereby maintaining itself in an operated position over a circuit which is independent of its initial energizing circuit. At its contacts 632, the relay R53?! opens the initial operating circuit for the seizure relay R5653, but this relay now remains locked up from ground applied to conductor CW3 upon the seizureof the selector 855. At its contacts $33, the relay prepares a point the circuit for operating the switching relay Riiiiii.

Each time the pulse relay R846 reoperates after the termination of each impulse, at its contacts 6%, it opens the initial operating circuit for the relay Rt fill; at its contacts 5-42, it recloses the energizing circuit for the hold relay R550; and, at its contacts EM, it recloses the loop circuit including the conductors C133 and CW2 to terminate each impulse transmitted to the selector 8H5. In the above described manner the relay R645] follows the series of impulses transmitted by the operator at the toll board sec, and repeats these impulses, at the contacts E i], to the selector Bit and the subsequent switches in the train in order to complete the 55 connection to the desired called subscriber line.

Referring to Fig. 8, it will be assumed that the digit dialed to control the selector M5 is the digit 8 and that the selector 8i5 has elevated its Wipers in a vertical direction to the eighth level, and has automatically rotated the wipers over the contacts of the associated level to select the trunk line 886 extending to the combination connector 825. The final two digits of the desired called subscriber number are now dialed by the operator and, in the manner described above, are repeated by the pulse relay Rii it in i order to control the operation of the connector 52 5. The connector 325 responds, in a well known manner, to raise its wipers to the level of its associated bank contacts terminating the line iiZt of the called subscriber substation A3 and, in response to the final digit dialed by the toll operator, rotates its wipers over the selected level into engagement with the set of bank contacts terminating the line 826.

If the desired called line is busy when the wipers of the connector 825 are positioned into engagement therewith, the usual busy tone signal is transmitted to the operator at the switchboard 398 to indicate that the called line cannot be signaled at the present time. It will be assumed, however, that the called line is idle when the wipers of the connector 325 are placed into engagement therewith, and the connector, in a well known manner, switches the connection through to the selected line. The ringing control of the combination connector 825, when utilized in a toll connection, is such that the connector does not automatically ring the desired called line but must be controlled by the operator at the toll board to signal the called subscriber.

When the connector 825 switches the connection through to the line 826, ground potential is removed from the conductor C183, thereby opening the circuit of the relay R559. The relay R566 now restores to normal and, at its contacts 555, connects ground potential by way of the contacts 863, 622, 613 and 565, to the conductor C183 in order to prepare the connector to ring the desired called subscriber line when ground potential is subsequently removed from the conductor C183 by the operation of the ring control relay R628, as will be described hereinafter. At its contacts 56L 562 and 563, the relay R550 removes the resistance 515 from the conductors C18! and C182 and reconnects battery and ground potentials by way of the relays R'i0 and R55? and the windings 554 and 555, to the conductors C182 and CTBI, respectively; and, at its contacts 566, it completes an operating circuit for the switching relay R525].

Upon operating, the relay R520, at its contacts 52l to 5524, inclusive, transfers the loop circuit including the conductors C48! and C482, from the windings of the pulse relay R640, to the windings 55! and 552 of the repeating coil 550 and the upper and lower windings of the supervisory relay EMS in series. The relay R540 operates at this time over a circuit including the cord circuit 3M and, at its contacts 5M, completes a. circuit for maintaining the pulse relay Ram in its operated osition to prevent the relays in the toll transmission trunk circuit 600 from restoring. It should be noted at this time that since the contacts 52| to 524, inclusive, are of the make-before-break variety, the relay R540 operates to close its contacts 54! before the relay EMS is restored to normal. As a further result of the operation of the relay R520, at its contacts 529, it prepares a circuit for operating the ring control relay RG20; at its contacts 525 it connects battery potential through the winding of the answer relay R570 in order to shunt out the battery potential applied thereto by way of the high resistance 5'52. At its contacts 525, the relay R520 removes ground potential from the control conductor C483 extending to the main exchange, and, at its contacts 521, it applies battery potential to the conductor C483. As a result of the latter operation a circuit is now completed which may be traced from ground, by way of the contacts i and 44!, the conductor C-iBl, the lower winding of the control relay R410, the conductor C 583, the lower winding of the control relay R5), the conductor C530, the contacts 5H5 of the busy key K5t5, the contacts 675 and 521, and the resistance 680, to battery.

As a result of the above traced circuit the relay Rl'll} in the toll trunk circuit 100 is operated, but the relay R510 in the toll transmission trunk 600 is not operated. More specifically, the circuit including the upper winding of the control relay RG75 is rendered ineffective since the circuit therefor may be traced from ground, conductor C687, the upper winding of the relay R413, and the resistance 412, to ground. No current flows through the upper winding of the relay and the current flow through its lower winding is sufficient to cause it to operate at this time. Referring to the control relay RENE, it is to be noted that when battery potential is connected to the conductor C539, a circuit is completed for its upper winding from ground, by way of the resistance 5M, and the upper winding of the relay R5), to battery potential connected to the conductor C530. A circuit is also completed for the lower winding of the relay in series with the lower winding of the control relay PAH] in the toll trunk circuit lfili. Since the windings of the relay R536 are in opposition to each other, and since the energizing circuit is completed for both windings, the relay does not operate at the present time.

The control relay Edit in the toll trunk circuit 46%? operates over the above traced circuit and, at its contacts all, it completes a circuit from ground, by way of the contacts and the lower winding of the relay Ri le, to battery. The relay R466 operates over the above traced circuit and completes a holding circuit including its upper winding, the contacts M8, and ground potential applied to the conductor C ifid; and, at its contacts 4 25, it opens the circuit of the seizure relay Ra a. As a further result of the operation of the relay R 140, at its contacts 43-2 it removes ground potential from the conductor C isti; and, at its contacts M3, it applies battery potential through the winding of the ring control relay R ilfi to the conductor 0386. At its contacts MI and 442, the relay R445 transfers the connection of ground potential to the conductor C lsl from contacts :35! to contacts 332.

When the ground potential is removed from the conductor C 536 upon the operation of the relay R4 18, the toll selector 336 operates to prepare the circuit including the talking conductors cast and C582 for transmission, and to return ground potential by way of the wiper and the conductor C436 in order to complete an operating circuit for the ring control relay R MS. Consequently', when ground potential is applied to the conductor C486 by the toll selector $333, the ring control relay PAH] operates and, at its contacts M2, applies a multiple grounsil potential to the conductor GMT. The relay B 535 which is of the slow-to-release type, subsequently restores to normal and, at its contacts removes the ground potential from the conductor C ie'i; however, ground potential is maintained thereon through the contacts MZ. At its contacts 33!, the relay R 335 prepares a point in the circuit for applying battery by way of the resistance to the conductor C487. The latter circuit, however, is not completed until the ring control relay Rd! is restored to normal.

At the present time the relays R558, R4 10, RQGQ and Bill? of the toll trunk circuit 285 are in their operated positions and the circuit is ready to respond to the control exercised by the toll operator to signal the called subscriber. It should be noted at this time that when the toll trunk circuit 6% functions to remove ground potential from the conductor the toll selector 338, in addition to returning ground potential to the control conductor C 386, also signaled the operator at the toll board 339 to in- 9 dicate that the connection had been extended to the line of the desired called subscriber and that it may now be signaled.

When the operator at the toll board 3% is ready to signal the called subscriber, she causes ground potential to be removed from the conductor (34%, whereupon the ring control relay R liil restores to normal. Upon restoring to normal, at its contacts l! L the relay Rtlll applies resistance battery potential to the conductor C te! and the conductor C583 over the fo1lowing circuit: batteiy, resistance lfill, contacts 13i, ill and M2, the conductor 6513?; one branch extending by way of the upper winding of the control relay R478 and the resistance 412, to ground, and the other branch extending by way of the lower winding of the relay Rd'lt, the conductor (M83, and the lower winding of the control relay R5), one branch extending by way of the upper winding of the relay R5! and the resistance 5M, to ground, and the other branch extending by way of the conductor C536, the contacts tilt, 615 and 521, and the resistance 689, to battery. In the above traced circuits it is to be noted that the lower winding of the control relay R l'ldis now shunted because the conductor C 18? is connected to resistance battery and the conductor C483 is also connected to resistance battery, but a circuit is now completed for the upper winding of the relay PAW by way of the resistance 412, to ground. In View of the foregoing, the relay R416 remains in its operated position. However, when resistance battery potential is applied to the conductor C 383 the lower winding of the relay R5Hi is shunted because resistance battery is also connected to the conductor C539 and a circuit is completed for the upper winding of the relay, which includes the resistance battery applied to conductor C535),

and ground through the resistance Md. The relay Edit now operates over the circuit including its upper winding and, at its contacts 5i i, completes a circuit which may be traced from ground by way of the contacts MI, 51! and 529, and the winding of the ring control relay RSZB, to battery. The ring control relay R626 operates over the above traced circuit and, at its contacts 522, removes ground potential from the conductor CW3, thereby causing the combination connector 25 to signal the substation A3 over the line 8528.

When the called subscriber answers by removing his receiver from his associated telephone instrument, the combination connector 825 functions, in a well known manner, to cause the operation of the answer relay R518 in the toll transmission trunk circuit Sill). When the relay B515 is operated in response to the called subscriber answering the connection, at its contacts 5H, it completes an operating circuit for the supervisory control relay RE I ii. The relay RE i 6, upon operating, at its contacts 612, reapplies ground potential to the conductor CW3 to terminate the ringing control operation of the combination conhector 825. As a further result of the operation, the relay R6), at its contacts El l, places a short circuit around the upper high resistance winding of the supervisory relay R5551. The shuntin of the high resistance upper winding of the relay R-Ia lll, in addition to improving the transmission qualities of the trunk line A30, also causes an answer signal to be given to the operator at the toll board 3% to indicate that the subscriber has answered the call.

When the toll operator receives the answer supervision she againcauses ground potential to be connectedto the conductor C486 and thus reoperates the relay R410. Upon operating, the rela R HO, at its contacts 4| I, removes the resistance battery potential from the conductor C487 and, at its contacts M2, it substitutes a direct ground potential. A circuit is now completed for the lower winding of the control relay R410 in order to maintain the relay in its operated posititon, but the circuit including its upper winding is of no efiect since the winding is shunted at this time. When ground potential is applied to the conductor C483 through the lower winding of the relay R 570, an energizing circuit is completed for the lower winding of relay R5lii which in cludes the resistance battery potential connected to the conductor C530 and an energizing circuit is also completed for the upper winding of the relay REM] by way of the resistance 5M and ground. However, since the windings of the relay R5!v are in opposition to each other, the abov traced circuit for both windings causes the relay to restore to its normal position at this time. When the relay Rfilfl restores to normal, at its contacts 5| I, it opens the operating circuit of the ring control relay R520. The relay R620 now restores to normal, and, at its contacts 622, again prepares the circuit for applying ground potential to the conductor C183 when ground is removed therefrom by restoration of the supervisory control relay R516.

The desired connection between the operator at the toll board 300 and the called subscriber at the substation A3 is now completed and the toll operator may withdraw from the connection to permit the distant calling subscriber to converse with the called subscriber at the substation At. It is to be noted that transmission current for the called station is supplied through the windings of the relays R510 and R551, and the transmission current for the calling end of the connection may be supplied from either the cord circuit 33! or from the toll selector 33$].

Recall supervision to the toll operator In the event that the toll operator at the distant toll board desires to communicate with the operator at the toll board 306, she may do so in any well known manner, such as, for example, transmitting ringing current over the toll line 319. When ringing current is transmitted over the toll line 3l9 a signal, at the toll board 300, is operated to indicate to the operator thereat that the distant toll operator desires to converse with her. The toll operator may now actuate a talk key (not shown) at her position in order to reconnect her telephone circuit to the toll line 3H3. After the toll operator at the toll board 309 receives the information from the distant toll operator she may remove her telephone circuit from the connection by restoring the talk key to its normal position.

In the event that the called subscriber at the substation A3 desires to communicate with the operator at the toll board 300, he may do so by momentarily actuating the switchhook at his telephone instrument a number of times. Attention is directed to the fact that the relay R519 in the toll transmission trunk circuit 600 is maintained in its operated position during the time that conversation takes place between the calling and called subscribers. Consequently, each time the called subscriber actuates the switchhook at the substation A3 the switching apparatus functions, in a well known manner, to interrupt the circuit of the answer relay R516. Each tim the relay R519 restores to normal, at its contacts 5', it

opens the circuit of the supervisorycontrol relay R6). Each time the relay R6? restores to normal, at its contacts SIS, it maintains a ground potential upon the conductor C183 extending to the selector 8|5; and, at its contacts 6% i, it removes the shunt from the high resistance upper winding of the supervisory relay R540.

It will be recalled that when the supervisory control relayRBiO was energized in response to the called subscriber answering the connection, the high resistance upper winding of the relay R540 was removed from the loop circuit including the talking conductors C481 and 0482, thereby to control a signal at the toll board 300 to indicate that the called subscriber answered the connection. When the high resistance upper winding of the relay R540 is intermittently reinserted in the above described circuit under control of the relay RGIO, it causes an intermittent signal to be given to the operator at the toll board 300 as an indication that the called subscriber at the substation A3 desires to communicate with her. The toll operator may reconnect her telephone circuit to the connection extending between the toll board 300 and the called subscriber at the substation A3 by actuating the talk key (not shown) at her position, and may then communicate with the called subscriber in a well known manner. After the toll operator has communicated with the called subscriber at the substation A3 she may again restore the talk key at her position in order to reestablish the connection between the calling subscriber in the distant exchange and the called subscriber at the substation A3.

Disconnect supervision After the conversation between the calling and the called subscriber has been terminated and the called subscriber at the substation A3 has restored his receiver upon the switchhook of his telephone instrument, the switching apparatus including the combination connector 825 and the selector 8|5 operates, in a well known manner, to open the circuit of the relays R510 and R551. The relay R510 restores to normal and, in the previously described manner, causes the relay RBIO to restore to normal and again insert the high resistance upper winding of the relay R540 into the loop circuit including the conductors C48! and C482. The insertion of the high resistance upper winding of the relay R540 into the above mentioned loop circuit causes a signal to be given to the operator at the toll board 300 as an indication that the called subscriber has disconnected. It is to be noted, however, that the switching apparatus, including the selector M and the combination connector 825, is not restored to normal at the present time due to the fact that ground potential is still maintained upon the conductor C184 by way of the contacts 663 and 613'.

Recalling the called subscriber In order to describe the manner in which the operator at the toll board 300 may resignal the called subscriber at the substation A3, it will be assumed that the subscriber at the substation A3 has prematurely restored his receiver upon the switchhook of his telephone instrument and that the toll operator at the distant toll board has resignaled the operator at the toll board Simand has informed her that the calling subscriber desires to be reconnected to the subscriber at the substation A3.

In order to re-ring the called subscriber at the substation A3, the operator at the toll board 300 controls the cord circuit 301 and the toll selector 330, in a well known manner, whereupon ground potential is removed from the conductor C486. Removal of ground potential from the conductor C486 opens the circuit of the ring control relay R410, whereupon this relay restores to normal and, at its contacts 4| I, reapplies resistance battery potential, over the previously described circuit, to the conductor C481. When battery potential is connected to the conductor C481, a circuit is completed by way of the upper winding of the relay R410 and resistance 412, to

ground, in order to maintain the relay in its operated position, and battery potential is extended by way of the lower winding of the relay and conductor C483 through the lower winding of the relay R5i0 to resistance battery connected to the conductor 0530. This circuit shunts the lower windings of the relays R410 and R5). Simultaneously with the completion of the above mentioned shunting circuit, a circuit may now be traced from the resistance battery applied to the conductor C530, by way of the upper winding of relay R5) and the resistance 5l4, to ground, whereupon the relay R5") operates and closes its contacts 5| I.

When the above mentioned contacts 5 are closed a circuit is completed from ground, by way of the contacts 651, 5!! and 529, and the winding of the ring control relay R620, to battery. The relay R620 operates over the above mentioned circuit and, at its contacts 622, it removes the ground potential applied to the conductor C183. Removal of ground potential from the conductor C183 controls the combination connector 825, in the previously described manner, to transmit ringing current over the called subscriber line 820.

When the called subscriber at the substation A3 responds by removing his receiver from the telephone instrument, the relays R510 and R551 are again operated and control the switching apparatus involved in the connection in order to transmit answer supervision to the operator at the toll board 300. When the operator at the toll board 300 receives the answer supervision, she again causes the cord circuit 301 and the toll selector 330 to apply ground potential to the conductor C435 and again operat the ring control relay R410. As has been mentioned above, operation of the relay R4l0 removes the resistance battery otential from the conductor C481 and substitutes a ground potential, whereupon the relay R5! 0 in the toll transmission trunk circuit 600 restores to normal and the relay R410 in the toll trunk circuit 400 remains in its operated position. Upon restoration, the relay R5|0, at its contacts 5| I, again opens the circuit of the ring control relay R528. The relay R620 now restores to normal and, at its contacts 622, reapplies ground potential to the conductor C183. The calling subscriber in the distant toll ofiice may now communicate with the called subscriber at the substation A3 and complete the conversation that was prematurely interrupted by the disconnection of the subscriber at the substation A3.

Release In order to describe the release of the connection established between the calling subscriber in the distant toll ofiice and the called subscriber at the substation A3, it will be assumed that when the called subscriber at the substation A3 replaced his receiver upon the switchhook of his telephone instrument, the calling subscriber in the distant toll office also replaced his receiver upon his telephone instrument. As a result of the latter operation the distant toll operator receives the usual disconnect supervision and thereupon breaks down the toll connection between the distant toll ofiice and the toll board 300. When the latter connection is taken down, the toll operator at the toll board 300 receives the usual disconnect supervision at the answer end of the cord circuit 3M, and since she has also received a disconnect supervision upon the called end of the cord circuit 3!] i she may now withdraw the cord circuit Sill from the jacks J3ll3 and Jstfi. When the plug P364 of the cord circuit 3M is withdrawn from the jack J3fi5, the toll selector 33G restores to normal in a well known manner, thereby removing ground potential from the conductors C485 and C485. As a further result of the restoration of the toll selector 330, the operating circuit, including the conductors and C 232, for the supervisory relay R546 in the toll transmission trunk circuit 600, is opened, whereupon the relay R549 restores to normal.

Referring now to the toll trunk circuit 490, it will be noted that when ground potential is removed from the conductor C586 the ring control relay R lld restores to normal and, at its contacts ill. reapplies the resistance battery potential to the conductor C48]. The reconnection of resistance battery potential to the conductor C li 'i completes a holding circuit including the upper winding of the relay R419 and the resistance M2, to ground, in order to maintain the relay amt in its operated position. The resistance battery potential connected by way of the lower winding of'the relay R410 to the conductor C4583 causes the relay RIU in the toll transmission trunk circuit Still to reoperate in the previously described manner.

When ground potential is removed from the conductor C485, the relay R46!) restores to normal and. at its contacts MM, completes a circuit from ground. by way of the contacts MI, 464 and 456, and the winding of the release relay R 129. to battery. The relay Rtzil operates over the above traced circuit and, at its contacts 422 and 5 24. applies ground potential to the conductors C584 and C 585, respectively, in order to maintain the toll trunk circuit 4!!!! busy in the banks of the selectors having access thereto. As a further result of the restoration of the relay R460. at its contacts AM, it prepares a circuit for the relay R lbll; and at its contacts M53, it o ens theinitial operating circuit for the lower winding of the relay RAM]. As a further result of the removal of ground potential from the conductor C485, the relay R441! also restores to normal. Upon restoring to normal, the relay E i-Ml, at its contacts M3, disconnects the relay R -ilil from the conductor C685; and, at its contacts 4M, it reapplies ground potential to the conductor C686 in order to prepare the toll trunk circuit can for subsequent seizure. At its contacts 442, the relay R 540 disconnects the re sistance battery potential applied to the conductor 048?; and, at its contacts 44!, substitutes therefor a ground potential applied by way of the contacts 45!. The substitution of ground potential to the conductor C481 completes a shunt c rcuit. around the upper winding of the relay new and it completes a holding circuit for the lower winding of the relay in order to maintain the relay in its operated position. The substitution of ground potential for the resistance battery potential to the conductor C 183 causes the relay 35m in the toll transmission trunk circuit 603 to restore to normal.

Referring now to the toll transmission trunk circuit iiil, it will be noted that when the relay REM restored'to normal as a result of the restoration of the toll selector 3%, at its contacts 5M, it opened a loop circuit including the upper and lower windings oi"- the pulse relay Rfitll. When the pulse relay R6 55] restores to normal, at its contacts 542, it opens the circuit of the hold relay R5559. At its contacts li -il, the relay Rii lil also disconnects the battery potential, ap plied by way of the winding of the relay RE'Hl, from the conductor CW2. Since the relay R650 is of the slow-to-release type, it subsequently restores to normal and, at its contacts 655, it opens the circuit for the relay The relay R650 is also of the slow-to-release type and, upon .restoring to normal at its contacts 66%, it disconnects ground potential, applied by way of the winding of the relay R551, from the conductor C'lili; at its contacts it opens a point in the initial operating circuit for the relay RMQ; and, at its contacts (563, it removes ground potential from the conductors C783 and 033 5.

Removal of ground potential from the conductor Clii l causes the selector 855 and the conhector 825 to restore their associated Wiper to their normal positions, whereupon the line 826 of the subscriber at the substation A3 is rendered available for further calls. As a further result of the restoration of the relay Rttlfil, at its contacts 663, it also opens the holding circuit of the relay The relay W339 now restores to normal and, at the contacts 633 opens the circuit of the relay R5525}. At its contacts 5335, the relay Rfifit opens a point in the holding circuit for itself; and. at its contacts 632, it prepares a point in the initial operating circuit for the relay R569.

Responsive to the opening of the holding circuit of theswitching relay Rt'iiii, the relay restores to normal and, at its contacts 5M to 52 3,

inclusive, it disconnects the left-hand windings of the repeating coil 559 from the trunk conductors C lti and our, and it connects these conductors to the windings of the pulse relay B5 5 3. At its contacts 525, the relay R52 2! disconnects the battery potential from the winding of the answer relay HEW, thereby removing the shunt circuit from around the high resistance M2; and, at its contacts 526 and 521, it disconnects the resistance battery potential applied to the conductor 653% and substitutes in place thereof a direct ground potential. Attention is directed to the fact that when the toll trunk circuit dill restored to normal, direct ground potential was applied by way of the lower winding of i the relay Rd!!! to the conductor 0- 583, and ex tending therefrom, by way of the lower winding of the relay Rfiifi, to the resistance battery potential applied to the conductor When the circuit including the lower windings of the relays Rdl'tl and R559 is energized in the above described manner, the relay Rdl'il remains in its operated position and the relay R556 restores to normal. Accordingly, when ground potential is substituted for the resistance battery potential applied to the conductor C530, the energizing circuit for maintaining the lower winding of the reslay Edit in its operated position is opened, thereby causing the latter relay to restore to normal.

It will be recalled that during the release op erations of the toll trunk circuit 4% the relay RENE! in the toll transmission trunk circuit 59%! was momentarily operated and restored to normal. Due to the fact that the ring control relay R6253 is of the slow-to-operate type, the momentary completion and interruption of its circuit at the contacts 51! does not permit suflicient time for the relay to operate. Accordingly, ground potential is maintained upon the conductor C183 during the releasing operations of the toll trunk circuit Ground potential is removed from the conductors C183 and C18 upon the restoration of the hold rela R660 in the manner previously described.

When the relay R i'ill restores to normal, in the above described manner, at its contacts 411, it opens the operating circuit for the release relay R62!) which also restores to normal. At its contacts 522 and 324, the relay R420, upon restoring to normal, removes the busy marking ground potentials from the conductors C584 and C485; and, at its contacts 42! and 523, it reconnects the windings of the operator relay R459, and the windings of the automatic relay R860 and seizure relay R438 to the conductors C484 and C585, respectively. The switching apparatus including the toll transmission trunk circuit 60!] and the toll trunk circuit tilt have now been restored to normal and may be selected by the operator at the toll board 306 to extend additional connectlons to the branch exchange 56.

ToLL CALL FROM A DIsTANT EXCHANGE EXTENDED BY THE TOLL OPERATOR TO THE BRANCH EXCHANGE OPERATOR FOR COMPLETION The manner in which toll calls are established by the toll operator in the main exchange by directly controlling the automatic switching apparatus in the branch exchange having been described above, a description will now be given of the operation of the switching apparatus when the toll operator in the main exchange 20 extends a toll connection to the manualoperator in the branch exchange 50 for completion. When the operator at the toll board 3M! desires to extend a toll call to the operator at the switchboard I685), she selects a toll selector, such as 330, and dials the digit 6, whereupon the toll selector raises its wipers to the sixth level and automatically rotates its wipers over the selected level to select an idle trunk line, such as 32!.

Accordingly, it will be assumed that the operator at the toll board 380 has received a toll call over the toll line 3l9 and has answered the call by inserting the plug P302 into the jack J303. It will also be assumed that the calling subscriber in the distant exchange desires to communicate with the subscriber at the substation A3 in the branch exchange 50. It will be understood that all of the automatic subscribers in the branch exchange may be called directly by the operator at the toll board 300; however, it is sometimes desirable to route such connections to the branch exchange operator for completion. For example, if the local subscriber at the substation A3 is going to be absent from his premises for a certain period of time, he may inform the branch exchange operator that he may be reached by extending a, connection to some other subscriber substation.

It will now be assumed that the toll operator has inserted the call plug 1 3% into the jack J 385, and has operated the toll selector 330, in the previously described manner, and that the selector 33% has selected the trunk line 32! extending to the toll trunk circuit 400. When the wipers 33! to 334, inclusive, of the toll selector 339 engage the contacts of the bank terminating the conductors of the trunk line 32!, ground potential is applied by way of the wiper 334, the conductor C484, the contacts 32! and 46!, and the winding of the operator relay R450, to battery. The relay R458 operates over the above traced circuit and, at its contacts 253, applies ground potential to the conductor C585 in order to busy the toll trunk circuit 450 in the banks of the toll selectors having access thereto. At the contacts 453, the relay R 359 also completes a circuit by way of the contacts 645 for operating the slow-to-release seizure relay R238. At its contacts 455, the relay R45!) dis-connects the automatic relay Rtfiil from the conductor C485; at its contacts etc, it opens a point in the circuit for the release relay R423; and, at its contacts 455, it prepares a point in the circuit for operating the relay Ride. As a further result of the operation of the relay R 150, at its contacts 45!, it disconnects direct ground potential from the conductor C481; and, at its contacts 452, it applies battery potential by way of the resistance 441 and the contacts 552 and 54!, to the conductor C481.

When the relay R438 operates over the above described circuit, at its contacts 43!, it opens a point in the incomplete circuit for applying resistance battery by way of the contacts 4! I to the conductor C581 and, at its contacts 432, it prepares a point in the circuit for subsequently applying ground potential to the conductor C481.

As a further result of the engagement of the wipers 335 to inclusive, with the trunk line 32!, a loop circuit is completed including the cord circuit 3M, the toll selector 339, the conduc tors CHM and C482, the contacts 522 and 524, and the lower and upper windings of the pulse relay R540, to battery and ground, respectively. The pulse relay R640 operates over the above traced loop circuit to control the toll transmission trunk circuit 698, in a manner to be explained hereinafter.

Attention is now directed to the fact that the control conductor ClSZi of the interexchange trunk line 48%, prior to the seizure of the toll trunk circuit 498, has ground potential applied thereto through the lower winding of the control relay R410 and through the lower winding of the control relay R5l9. This circuit may be traced from ground, by Way of the contacts 45! and 44!, the conductor C l81, the lower winding of the relay R418, the conductor case, the lower winding of the control relay R556, the conductor 0530, the contacts 5H3 of the key K5l5, and the contacts 515 and 526, to ground. In View of the above circuit the lower windings of the relays R 310 and R5!!! are not,energized. It should also be noted that ground potential is connected to the upper winding of the relay R410 by way of the resistance 412, and that ground potential is connected to the upper winding of the relay R5! 0 by way of the resistance 5 4,

When the toll trunk circuit 400 is seized and the relay R450 operates, a resistance battery potential is applied to the conductor C481 from battery, by way of the resistance 461, and the contacts 452 and 44!. When resistance battery potential is substituted for the ground potential applied to the conductor C481, a circuit is completed for energizing the upper and the lower windings of the relay R416. The circuit for the upper winding may be traced from ground, by

i7 way of the resistance 412 and the upper winding of the relay RMO; and the circuit for the lower winding of the relay may be traced from the ground potential applied to the conductor C433 at the toll transmission circuit one and the lower winding of the relay Rili). Since the windings of the relay Rdlil are in opposition to one another, the above traced energizing circuits for these windings prevent the relay from operating at this time. However, in the toll transmission trunk circuit 680, the application of resistance battery to the conductor C483 by the toll trunk circuit Add completes a circuit for energizing the lower winding of the relay Rlil. This circuit may be traced from ground, by way of the contacts 526, 515 and 596, the conductor G538 and the lower winding of the relay REM, to battery potential applied to the conductor C483. A branch of this circuit is also extended by way of the upper winding of the relay Rliiil, and the resistance did, to ground. The latter circuit, however, since it is traced from ground to ground, does not have any eir'ect upon the upper Winding of the relay. The relay R516 now operates as a result of the energizing circuit completed through its lower winding and, at its contacts 51 l, prepares a circuit for the upper winding of the transfer relay R61 ll.

When the pulse relay Riidii operates over the previously traced loop circuit, including the conductors C iSi and C482, at its contacts 6 21, it applies battery potential by way of the high resistance 512, the winding of the relay R5163, th winding 55 3 of the repeating coil 55%, and the contacts 56!, 6M and Eli, to the conductor 0182. The latter circuit, as has been pointed out hereinbefore, prepares a point in the circuit for controlling the selector 815. However, as will be pointed out, the relay R610 will subsequently be operated to disconnect the above traced circuit from the conductor C182. As a further result of the operation of the relay Rteil, at its contacts 642, it completes an operating circuit for the s1ow-to-release hold relay R650; and, at its contacts M3, it opens a point in the incomplete circuit for subsequently operating the relay R635]. The relay R656, upon operating, at its contacts 65L completes an obvious circuit for operating the relay Riifiil and also completes a circuit from ground by way or the contacts Bill, 5!! and 523 for energizing the upper winding of the transfer relay R616.

The relay R610 operates when the above traced energizing circuit is completed for its upper winding and, at its contacts 518, it prepares a locking circuit for its lower winding. As a further result of the operation of the relay new, at its contacts 611 and 613 it disconnects the talking conductors extending from the right-hand windings of the repeating coil 55!] from the conductors 018i and C182, and connects the right-hand windings of the repeating coil 5% by way of its contacts 612 and 614, thereby to prepare a circuit for extending the connection to the jack J1E at the switchboard ltbil. At its contacts 615, the relay R610 disconnects the direct ground potential from the conductor 053i) and, at its contacts 618, it connects battery by way of the resistance 6%, and the contacts 616 and 516 to conductor C539. At its contacts 811, the relay R610 prepares a circuit for the upper winding of the relay Rl lil; at its contacts 619, it opens a point in the operating circuit for the relay Rfitii; at its contacts 612 and 813 it disconnects the conductors C183 and C134 from the toll transmission trunk 18 circuit 600; and, at its contacts fill it prepares a point in the holding circuit for the relay R120. At its contacts 614', the relay R610 completes a circuit from ground by way of the contacts 614 and the winding of the switching relay R520, to battery.

It will be recalled that the relays R660 and R510 operated when the hold relay R650 closed its contacts Edi. As a result of the operation of the relay R668, at its contacts 66!, it closed a point in the circuit of the conductor C18! which, however, has no effect at this time since the relay R61 ll has operated. At its contacts 662, it prepares a point in the incomplete circuit for operating the relay R533; and, at its contacts 683, it completes a holding circuit for the relay R618 which may be traced from ground, by way or" the contacts 663 and 618, and the lower winding of the relay-R615), to battery.

The latter relay will now remain in its operated position, even though the circuit for its upper winding is subsequently disconnected.

Before discussing the operation of the relay Rims, a description will now be given of the effect of the substitution of resistance battery for ground potential to the conductor 0530 as a result of the closure of the contacts 616 by the relay R618. When resistance battery potential is applied to the conductor C536, one branch of the circuit extends by way of the upper winding of the relay Riilll and resistance 514, to ground, whereupon the upper winding is energized; and another branch of the circuit extends by way of the lower winding of the relay REM], the conductor C 183, and the lower winding of the relay R lld to resistance battery connected to the conductor 0M1. In this circuit the lower windings of the relays R410 and Rliifl are shunted and therefore the lower windings or these relays are not energized. A circuit is now, however, completed for the upper winding of the relay R4111 which may be traced from the resistance battery applied to the conductor C481 through the upper windin of the relay R410 and the resistance 412, to ground.

The relay R410 operates as a result of the above traced energizing circuit for its upper winding and the relay Riilil remains in its operated position as a result of the above traced energizing circuit for its upper winding.

As a result of the operation of the relay R4123, at its contacts 41! it completes a circuit which may be traced from ground by way of the contacts fill, 454 and 155, and the lower winding of the relay RNA], to battery. Relay Redd operates *over the above traced circuit and, at its contacts s45, disconnects the seizure relay R436 from ground at contacts and, at its contacts M6, it connects its upper winding to ground at contacts 4 53. The latter circuit maintains the relay R440 in its operated position even though the circuit for its lower winding is subsequently opened by the restoration of the relay R l'iii. As a further result of the operation of the relay R449, at its contacts Add, it removes ground potential from the conductor can; and, at its contacts M3, it applies battery potential through the winding of the ring control relay RM!) to the conductor C488. At its contacts Hi and M2, the relay R idil transfers the connection to the conductor OM31 from resistance battery potential to ground potential at the contacts 432.

When. ground potential is applied to the conductor (3481, the upper winding. of the relay R416 is short-circuited and an energizing circuit is completed for the lower winding 01 the relay in 

